Refining of hydrocarbon distillates



Nov. 23, 194s.v

. LB. HEMD REFINING OF HYDROCARBON DISTILLATES Filed sept. 29, 1945 be between about 10 to about 50 pounds per square inch.

In the case illustrated herein, tower 3 comprises a batch-type operation, in which operation the tower is nlled to the desired level with a solution of alkaline earth metal hydroxide and the gasoline is passed therethrough. The operation is continued until the alkaline earth metal hydroxide solution becomes spent for the purpose intended. In general, the consumption of alkaline earth metal hydroxide will be about one pound per 100 to 200 barrels of gasoline treated, depending upon the percentage of acidic bodies in the gasoline undergoing treatment. After the reagent becomes spent, the spent reagent is withdrawn and a new supply of reagent is charged to the tower. The particular case illustrated comprises a prewash tower containing a packing material to insure intimate contacting of gasoline and reagent. Any suitable packing material which does not react with the solution in tower 3 may be employed; a particularly suitable packing material comprising carbon Raschig rings. Other suitable packing materials may be employed such as bubble trays, baille plates, etc.

In the case of a batch-type operation as illustrated in the drawing, the spent alkaline earth metal hydroxide solution may be withdrawn from the lower portion of zone 3 through line 4 and valve 5, to disposal as desired.

In the case of continuous-type operation, the alkaline earth metal hydroxide may be continuously or intermittently withdrawn from the bottom of tower 3, supplied to the solution tank, not illustrated, wherein it is maintained at the desired concentration and then recirculated to the upper portion of tower 3.

An insoluble precipitate, comprising alkaline earth metal hydroxide and naphthenic and/or aliphatic acids, forms in tower 3, thus preventing the acids from entering the subsequent caustic treating step and causing undesired foaming therein. In the absence of such a pretreatment,

these acids form gels in the caustic solutions and4 result in foaming and caustic carryover from the caustic treating tower. The caustic solution becomes a soapy mass of bubbles and will not separate from the gasoline, with the result that the caustic solution is carried over with the gasoline to the gasoline storage facilities. v

When the gasoline also contains hydrogen sulfide, it preferably is given a preliminary caustic wash to remove hydrogen sulfide and this may be accomplished, in the case herein illustrated, by passing the gasoline from tower 3 through line 6 and valve 'I to caustic scrubber 8. Scrubber 8 is illustrated as the same general type as tower 3, it being understood that it may comprise any suitable other mixing and contacting apparatus. In this tower, hydrogen sulde reacts with the sodium hydroxide to form sodium sulfide. The caustic employed is preferably of to 15 B. grav-- ity. The caustic containing the sullide may be withdrawn from the lower portion of scrubber 8 through line 9 and valve IllI to storage or elsewhere as desired, and the gasoline, free from hydrogen sulfide, is withdrawn from the upper portion of tower 8 through line I I.

Several other modifications not illustrated are also comprised within the scope of the present invention. In one modication the prewash and caustic scrubbing may be effected n a common Zone by utilizing a mixture of alkaline earth metal hydroxide and caustic. In this case, caustic scrubber 8 may be omitted and the prewashed gasoline may be supplied from line 6 through line I2 and valve I3 direct to the absorber |4. When the gasoline is free from hydrogen sulfide or has been otherwise treated to remove the hydrogen sulde, caustic scrubber 8 may be omitted and the prewashed gasoline passed through line I2 and valve I3 direct to absorber I4.

Caustic scrubbing in zone may be effected at substantially atmospheric temperature and under suflicient pressure to effect movement of the gasoline through the system. The partially treated gasoline from line II, in one embodiment of the invention, is passed through valve I5 to heater I6. Heater I6 may comprise any suitable means for raising the temperature of the gasoline to about -'185 F. and thus may comprise a heat exchanger or externally fired heater. The heated gasoline is then passed through line I1 and valve I8 to absorber I4.

In another modication the partially treated gasoline from line II which is at substantially atmospheric temperature, may be passed through by-pass line I9, valve 2|), line I'I and valve I8, to absorber I4, and the mercaptan removal effected at substantially atmospheric temperature.

In the case here illustrated, absorber I4 comprises a packed tower of the same general design as towers 3 and 8, and the gasoline iscountercurrently contacted with the caustic solution therein. It is understood that any other suitable con tacting means may be employed within the scope of the invention. The gasoline substantially free of mercaptans is removed from the upper portion of absorber I4 through line 2| and valve 22 to storage or any further treatment as desired.

The spent caustic solution from absorber I4 is withdrawn from the lower portion thereof through line 23 and valve 24 and is partially heated in exchanger 25, directed through line 26 and valve 21 to heater 28 and then passed through line 29 and valve 3|) to regenerator 3|. Heater 28 may be of any desired design and thus may comprise a suitable heat exchanger or externally fired heater in order to raise the temperature of the spent caustic solution to that suitable for eifecting regeneration. In general, the temperature employed in regenerator 3| will be just below the boiling point of the solution and will, of course, vary with the gravity of the particular solution being employed. In general, the gravity of the solution employed in absorber I4 will be of l5 to 35 B. and the temperature in-regenerator 3| will be about 220 to about 250 F.

In the case illustrated, regenerator 3| is of similar design to absorber I4 and contains' a suitable packing material, it being understood that other suitable regenerating means may be employed. To eiect regeneration of the caustic solution and the separation thereof from mercaptans, steam or other suitable stripping medium is introduced through line 32 containing valve 33. An overhead stream comprising vaporous mercaptans and water is withdrawn from the upper portion ofregenerator 3| through line 34 and valve 35. The

regenerated caustic solution is withdrawn from the lower portion of regenerator 3| through line 38 and valve 3l, and is directed through heat eX- changer 25, line 38 and valve 39 to pump 40, by means of which it is directed through line 4| and valve 42 to cooler 43. In cooler 43, the regenerated caustic solution is cooled to the desired temperature which in one embodiment of the invention is substantially atmospheric temperature and in another embodiment of the invention is between r 135 and 185 F. The cooled regenerated caustic is then directed through line 44, containing valve 45, to the upper portion of absorber I 4, for further use in the manner hereinbefore set forth.

While the description hereinbefore set forth has been directed primarily to aqueous solutions of alkali metal hydroxides, the features of the present invention are also applicable to the treatment of non-aqueous solutions of alkali metal hydroxides, such as alcoholic solutions, and also to alkali metal hydroxide solutions containing a modifying agent such as the well-known Unisol process in which the treating solution comprises a mixture of caustic and methanol, as well as alkali metal hydroxide solutions containing solutizers, such as tripotassium phosphate, potassium isobutyrate, alkanol amines, etc.

The following example is introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

A gasoline obtained by thermally cracking North Texas topped crude and containing 0.025% mercaptan sulfur, 0.04% by weight of naphthenic Y acids and phenols and a trace of hydrogen sulfide is rst passed in contact with barium hydroxide solution to remove the naphthenic acids. The gasoline is then scrubbed with a 12 B. caustic solution to remove the last traces of hydrogen sulfide, after which the gasoline is treated with caustic of B. in a process of substantially the design illustrated in the drawing to remove mercaptans.

Prior to the use of the barium hydroxide pretreatment, foaming occurred in the mercaptan absorber with the result that the gasoline withdrawn therefrom contained caustic solution. However, when utilizing the barium hydroxide pretreat, no foaming was encountered and ready separation of the treated gasoline was effected.

I claim as my invention:

1. A process for rening hydrocarbon distillate containing mercaptans, hydrogen sulde and an amount of carboxylic acids such that objectionable foaming occurs in the contacting of the distillate with caustic solution of a strength to remove the mercaptans, which comprises treating said distillate with a solution comprising a mixture of barium hydroxide and caustic of 5 to 15 B. to remove hydrogen sulfide and carboxylic acids, and thereafter treating said distillate with a caustic solution of 15 to 35 B. to remove mercaptans.

2. The process of claim 1 further characterized in that said distillate comprises gasoline.

JACOB BENJAMIN HEID.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,709,203 Black et a1 Apr. 16, 1929 1,953,336 Campbell Apr. 3, 1934 1,969,694 Hall Aug. 7, 1934 2,030,245 Crosby Feb. 11, 1936 2,057,918 Ridgway Oct. 20, 1936 2,066,925 Yabroff et al Jan. 5, 1937 2,112,313 Sewers Mar. 29, 1938 2,152,166 Yabroi Mar. 28, 1939 

